U.S. patent application number 10/980237 was filed with the patent office on 2005-05-12 for liquid crystal display device.
Invention is credited to Asakura, Toshiki, Kubo, Chikae, Ochiai, Takahiro.
Application Number | 20050099573 10/980237 |
Document ID | / |
Family ID | 34544442 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050099573 |
Kind Code |
A1 |
Kubo, Chikae ; et
al. |
May 12, 2005 |
Liquid crystal display device
Abstract
The present invention provides a liquid crystal display device
which can sufficiently reduce coloring even in an intermediate gray
scale display, not to mention, coloring in a white display state.
Pixel regions are formed between respective substrates with liquid
crystal filled therebetween, a projection pattern or a groove
pattern which divides each pixel region into a plurality of domains
is formed parallel to liquid-crystal-side surfaces of the
respective substrates, and the inclination of the projection
pattern or the groove pattern differs among red pixels, green
pixels and blue pixels.
Inventors: |
Kubo, Chikae; (Mobara,
JP) ; Asakura, Toshiki; (Togane, JP) ; Ochiai,
Takahiro; (Chiba, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
34544442 |
Appl. No.: |
10/980237 |
Filed: |
November 4, 2004 |
Current U.S.
Class: |
349/146 |
Current CPC
Class: |
G02F 1/133707 20130101;
G02F 1/134309 20130101; G02F 1/1393 20130101 |
Class at
Publication: |
349/146 |
International
Class: |
G02F 001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2003 |
JP |
2003-377912 |
Claims
What is claimed is:
1. A liquid crystal display device comprising: a pair of
substrates; a liquid crystal layer disposed between the pair of
substrates; and a plurality of pixel regions, wherein, each pixel
region includes a projection pattern or a groove pattern which
divides each pixel region into a plurality of portions, and an
inclination of the projection pattern or the groove pattern in at
least one of red pixel, green pixel and blue pixel is made
different from an inclination of the projection pattern or the
groove pattern in other color pixels.
2. A liquid crystal display device according to claim 1, wherein
the inclination of the projection pattern or the groove pattern
differs among the red pixel, the green pixel and the blue pixel
respectively.
3. A liquid crystal display device according to claim 1, wherein
the inclination of the projection pattern or the groove pattern of
the blue pixel is larger than the inclination of the projection
pattern or the groove pattern of the red pixel and the green
pixel.
4. A liquid crystal display device according to claim 1, wherein
the inclination of the projection pattern or the groove pattern of
the blue pixel is smaller than the inclination of the projection
pattern or the groove pattern of the red pixel and the green
pixel.
5. A liquid crystal display device according to claim 1, wherein
the inclination of the projection pattern or the groove pattern of
the pixels is set to satisfy any one of following relationships. 1)
blue pixel<red pixel<green pixel 2) blue pixel>red
pixel>green pixel 3) red pixel<blue pixel<green pixel 4)
green pixel<blue pixel<red pixel
6. A liquid crystal display device according to claim 1, wherein
electrodes are formed on liquid-crystal-side surfaces of both of
the pair of substrates, and a light modulation state of the liquid
crystal layer is controlled in response to a voltage applied
between the electrodes.
7. A liquid crystal display device according to claim 6, wherein
orientation films are formed on the liquid-crystal-layer-side
surfaces of both of the pair of substrates and the orientation
films are formed of a vertical orientation film.
8. A liquid crystal display device according to claim 1, wherein
the projection pattern or the groove pattern is a linear
pattern.
9. A liquid crystal display device according to claim 8, wherein
each pixel region is divided into two halves in the up-and-down
direction and the direction of the projection pattern or the groove
pattern is changed at a boundary line for dividing each pixel into
halves.
10. A liquid crystal display device according to claim 8, wherein
each pixel region is divided into multiple portions in the
up-and-down direction and the direction of the projection pattern
or the groove pattern is changed at boundary lines for dividing
each pixel into the multiple portions.
11. A liquid crystal display device comprising: a pair of
substrates; a liquid crystal layer disposed between the pair of
substrates; and a plurality of pixel regions, wherein, each pixel
region includes a projection pattern or a groove pattern which
divides each pixel region into a plurality of portions, and a
distance between projections of the projection pattern or a
distance between grooves of the groove pattern in at least one of
red pixel, green pixel and blue pixel is made different from a
distance between projections of the projection pattern or a
distance between grooves of the groove pattern in other color
pixels.
12. A liquid crystal display device according to claim 11, wherein
electrodes are formed on liquid-crystal-side surfaces of both of
the pair of substrates, and a light modulation state of the liquid
crystal layer is controlled in response to a voltage applied
between the electrodes.
13. A liquid crystal display device according to claim 11, wherein
orientation films are formed on liquid-crystal-layer-side surfaces
of both of the pair of substrates and the orientation films are
formed of a vertical orientation film.
14. A liquid crystal display device according to claim 11, wherein
the projection pattern or the groove pattern is a linear
pattern.
15. A liquid crystal display device according to claim 14, wherein
each pixel region is divided into two halves in the up-and-down
direction and the direction of the projection pattern or the groove
pattern is changed at a boundary line for dividing each pixel into
halves.
16. A liquid crystal display device according to claim 14, wherein
each pixel region is divided into multiple portions in the
up-and-down direction and the direction of the projection pattern
or the groove pattern is changed at boundary lines for dividing
each pixel into the multiple portions.
17. A liquid crystal display device comprising: a pair of
substrates; a liquid crystal layer disposed between the pair of
substrates; and a plurality of pixel regions, wherein, a plurality
of strip-like electrodes are formed in each pixel region, and an
inclination of the strip-like electrodes in at least one of red
pixel, green pixel and blue pixel is made different from an
inclination of the strip-like electrodes in other color pixels.
18. A liquid crystal display device according to claim 17, wherein
the inclination of the strip-like electrodes differs among the red
pixel, the green pixel and the blue pixel respectively.
19. A liquid crystal display device according to claim 17, wherein
the inclination of the strip-like electrodes of the blue pixel is
larger or smaller than the inclination of the strip-like electrode
of the red pixel and the green pixel.
20. A liquid crystal display device according to claim 17, wherein
the inclination of the strip-like electrodes is set to satisfy any
one of following relationships. 1) blue pixel<red pixel<green
pixel 2) blue pixel>red pixel>green pixel 3) red
pixel<blue pixel<green pixel 4) green pixel<blue
pixel<red pixel
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a liquid crystal display
device.
[0002] As a liquid crystal display device which adopts respective
substrates which are arranged to face each other in an opposed
manner with liquid crystal therebetween as an envelope, there has
been known a liquid crystal display device which, in each pixel
region of each substrate, uses a light transmitting conductive film
which is formed on a liquid-crystal-side surface of one substrate
as a pixel electrode and a light transmitting conductive film on a
liquid-crystal-side surface of another substrate as a counter
electrode.
[0003] Further, there has been also known a color liquid crystal
display device which is configured such that molecules of the
liquid crystal are vertically arranged between both substrates when
an electric field is not applied between the pixel electrode and
the counter electrode and the inside of one pixel is divided into a
plurality of domains by a projection pattern and slits formed on
the liquid-crystal-side surfaces of the respective substrates.
[0004] With respect to the liquid crystal, even when the molecular
arrangement is in an equal state, the double refractive index has
chromatic dispersion and hence, there arises difference among the
transmissivities of the respective pixels of red (R), green (G) and
blue (B) thus giving rise to coloring of an image. By making the
arrangement directions of the liquid crystal molecules in
respective domains different from each other, the coloring of the
image can be overcome.
[0005] In this case, with respect to the respective pixels
allocated to red (R), green (G) and blue (B), to overcome the
phenomenon that the transmissivity of the blue (B) pixel becomes
lower than the transmissivities of the red (B) and green (G) pixels
and hence, the whole screen is tinted in a yellowish color in a
white display state, Japanese Patent Laid-Open No. 267079/2000
discloses a technique in which, among the respective pixels, a
width of the slits formed in one pixel is made different from a
width of the slits formed in other pixels.
BRIEF SUMMARY OF THE INVENTION
[0006] Here, the liquid crystal display device having such a
constitution makes use of the fact that the transmissivity of the
pixel is changed corresponding to the width of the slits, wherein
the transmissivity is lowered by setting the width of the slits
formed in the given pixel to a given width or less, for example, 10
.mu.m or less.
[0007] However, in this case, the B-V characteristics which
indicate the brightness with respect to the voltage differ
corresponding to widths of slits of respective pixels and hence, in
an intermediate gray scale which is a region where a voltage served
for display is lower than a voltage for white, a drawback that
so-called coloring cannot be sufficiently overcome still
remains.
[0008] The present invention has been made under such circumstances
and it is an object of the present invention to provide a liquid
crystal display device which can sufficiently reduce coloring even
with respect to a display in an intermediate gray scale, not to
mention, a display in a white display state.
[0009] To explain the summary of the representative inventions
among the inventions disclosed in this specification, they are as
follows.
[0010] (1) The present invention is, for example, directed to a
liquid crystal display device which includes a liquid crystal layer
formed between a pair of substrates, a plurality of pixel regions,
and a projection pattern or a groove pattern which is formed in
each pixel region for dividing the pixel region into a plurality of
portions,
[0011] wherein, an inclination of the projection pattern or the
groove pattern in at least one of red pixel, green pixel and blue
pixel is made different from an inclination of the projection
pattern or the groove pattern in other color pixels.
[0012] (2) The present invention is, for example, on the premise of
the constitution (1), characterized in that the inclination of the
projection pattern or the groove pattern differs among the red
pixel, the green pixel and the blue pixel respectively.
[0013] (3) The present invention is, for example, on the premise of
the constitution (1), characterized in that the inclination of the
projection pattern or the groove pattern of the blue pixel is set
larger or smaller than the inclination of the projection pattern or
the groove pattern of the red pixel and the green pixel.
[0014] (4) The present invention is, for example, on the premise of
the constitution (1), characterized in that the inclination of the
projection pattern or the groove pattern of the pixels is set to
satisfy any one of following relationships.
[0015] 1) blue pixel<red pixel<green pixel
[0016] 2) blue pixel>red pixel>green pixel
[0017] 3) red pixel<blue pixel<green pixel
[0018] 4) green pixel<blue pixel<red pixel
[0019] (5) The present invention is, for example, directed to a
liquid crystal display device which includes a liquid crystal layer
formed between a pair of substrates, a plurality of pixel regions,
and a projection pattern or a groove pattern which is formed in
each pixel region for dividing the pixel region into a plurality of
portions,
[0020] wherein a distance between projections of the projection
pattern or a distance between grooves of the groove pattern in at
least one of red pixel, green pixel and blue pixel is made
different from a distance between projections of the projection
pattern or a distance between grooves of the groove pattern in
other color pixels.
[0021] (6) The present invention is, for example, on the premise of
any one of the constitutions (1) to (5), characterized in that the
groove pattern is constituted of an electrode forming portion and
an electrode non-forming portion.
[0022] (7) The present invention is, for example, on the premise of
any one of the constitutions (1) to (6), characterized in that
electrodes are formed on liquid-crystal-side surfaces of both of
the pair of substrates, and a light modulation state of the liquid
crystal layer is controlled in response to a voltage applied
between the electrodes.
[0023] (8) The present invention is, for example, on the premise of
the constitution (7), characterized in that orientation films are
formed on the liquid-crystal-layer-side surfaces of both of the
pair of substrates and the orientation films are formed of a
vertical orientation film.
[0024] (9) The present invention is, for example, directed to a
liquid crystal display device which includes a liquid crystal layer
formed between a pair of substrates, a plurality of pixel regions,
and a plurality of the strip-like electrodes which are formed in
each pixel region,
[0025] wherein, an inclination of the strip-like electrodes in at
least one of red pixel, green pixel and blue pixel is made
different from an inclination of the strip-like electrodes in other
color pixels.
[0026] (10) The present invention is, for example, on the premise
of the constitution (9), characterized in that the inclination of
the strip-like electrodes differs among the red pixel, the green
pixel and the blue pixel respectively.
[0027] (11) The present invention is, for example, on the premise
of the constitution (9), characterized in that the inclination of
the strip-like electrodes of the blue pixel is set larger or
smaller than the inclination of the strip-like electrode of the red
pixel and the green pixel.
[0028] (12) The present invention is, for example, on the premise
of the constitution (9), characterized in that the inclination of
the strip-like electrodes is set to satisfy anyone of following
relationships.
[0029] 1) blue pixel<red pixel<green pixel
[0030] 2) blue pixel>red pixel>green pixel
[0031] 3) red pixel<blue pixel<green pixel
[0032] 4) green pixel<blue pixel<red pixel
[0033] (13) The present invention is, for example, directed to a
liquid crystal display device which includes a liquid crystal layer
formed between a pair of substrates, a plurality of pixel regions,
and a plurality of strip-like electrodes which are formed in each
pixel region,
[0034] wherein a distance between the strip-like electrodes in at
least one of red pixel, green pixel and blue pixel is made
different from a distance between the strip-like electrodes in
other color pixels.
[0035] (14) The present invention is, for example, on the premise
of any one of the constitutions (9) to (13), characterized in that
the strip-like electrodes have a function of generating an electric
field having components in the direction parallel to the
substrates.
[0036] Here, the present invention is not limited to the
above-mentioned constitutions and various modifications are
conceivable without departing from the technical concept of the
present invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0037] FIG. 1A and FIG. 1B are views showing one embodiment of a
pixel of a liquid crystal display device according to the present
invention, wherein FIG. 1A is a plan view and FIG. 1B is a
cross-sectional view;
[0038] FIG. 2 is a characteristic graph showing the relationship
between the change of an electrode angle and the transmissivity of
the pixel of the liquid crystal display device according to the
present invention corresponding to red, green and blue pixels
(liquid crystal gap: 4.0 .mu.m);
[0039] FIG. 3 is a characteristic graph showing the relationship
between the change of an electrode angle and the transmissivity of
the pixel of the liquid crystal display device according to the
present invention corresponding to red, green and blue pixels
(liquid crystal gap: 4.2 .mu.m);
[0040] FIG. 4 is a characteristic graph showing the relationship
between the change of an electrode angle and the transmissivity of
the pixel of the liquid crystal display device according to the
present invention corresponding to red, green and blue pixels
(liquid crystal gap: 4.5 .mu.m);
[0041] FIG. 5 is a view obtained by plotting the change of an
electrode angle of the pixel of the liquid crystal display device
according to the present invention on a characteristic graph based
on CIE1931;
[0042] FIG. 6A and FIG. 6B are views showing another embodiment of
a pixel of a liquid crystal display device according to the present
invention, wherein FIG. 6A is a plan view and FIG. 6B is a
cross-sectional view;
[0043] FIG. 7A and FIG. 7B are views showing another embodiment of
a pixel of a liquid crystal display device according to the present
invention, wherein FIG. 7A is a plan view and FIG. 7B is a
cross-sectional view;
[0044] FIG. 8 is a plan view showing another embodiment of a pixel
of a liquid crystal display device according to the present
invention;
[0045] FIG. 9 is a plan view showing another embodiment of a pixel
of a liquid crystal display device according to the present
invention;
[0046] FIG. 10 is a cross-sectional view taken along a line X-X in
FIG. 1; and
[0047] FIG. 11 is a cross-sectional view taken along a line XI-XI
in FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0048] Embodiments of a liquid crystal display device according to
the present invention are explained hereinafter in conjunction with
attached drawings.
[0049] FIG. 1A is a plan view showing one embodiment of the
constitution of a pixel of a liquid crystal display device
according to the present invention. In FIG. 1A, the pixel is
configured such that three respective pixels for red (R), green (G)
and blue (B) which constitute unit pixels for color display are
arranged from the left side to the right side in the drawing. Here,
FIG. 1B is a cross-sectional view taken along a line b-b in FIG.
1A.
[0050] In these respective pixels, their constitutions are
substantially equal and hence, the explanation is made by focusing
on the constitution of the pixel for blue (B) and the pixel for red
(R) and the pixel for green (G) are further explained with respect
to the points which make the constitutions of the pixel for red (R)
and the pixel for green (G) different from the constitution of the
pixel for blue (B).
[0051] On a liquid-crystal-side surface of a transparent substrate
SUB1, first of all, gate signal lines GL which extend in the x
direction and are arranged in parallel in the y direction are
formed.
[0052] These gate signal lines GL surround a rectangular region
together with drain signal lines DL which will be described later
and the region constitutes one pixel region.
[0053] On a surface of the transparent substrate SUB1 on which the
gate signal lines GL are formed in this manner, an insulating film
GI made of SiN, for example, is formed in a state that the
insulating film GI also covers the gate signal lines GL (see FIG.
1B).
[0054] The insulating film GI has a function of an interlayer
insulating film with respect to the gate signal lines GL in a
region where the drain signal lines DL are formed and a function of
a gate insulating film in a region where a thin film transistor TFT
which will be explained later is formed.
[0055] A semiconductor layer AS made of amorphous Si, for example,
is formed on a surface of the insulating film GI in a state that
the semiconductor layer AS is overlapped to portions of the gate
signal lines GL.
[0056] The semiconductor layer AS is of a semiconductor layer of
the thin film transistor TFT, wherein by forming a drain electrode
DT and a source electrode ST on an upper surface of the
semiconductor layer AS, it is possible to constitute a MIS (Metal
Insulator Semiconductor) type transistor having the inversely
staggered structure which adopts a portion of the gate signal line
GL as a gate electrode GT.
[0057] Here, the drain electrode DT and the source electrode ST are
configured to be formed simultaneously at the time of forming the
drain signal line DL.
[0058] That is, each one of the drain signal lines DL which extend
in the y direction and are arranged in parallel in the x direction
has a portion thereof extended to the upper surface of the
semiconductor layer AS. The source electrode ST is formed in a
spaced-apart-manner from the drain electrode DT by a length of a
channel of the thin film transistor TFT.
[0059] The source electrode ST slightly extends to reach an upper
surface of the insulating film GI on a pixel region side from a
surface of the semiconductor layer AS and a contact portion which
establishes the connection between a drain electrode DT and a pixel
electrode PX described later is formed.
[0060] On the surface of the transparent substrate SUB1 on which
the thin film transistors TFT, the drain signal lines DL, the drain
electrodes DT and the source electrodes ST are formed in this
manner, a protective film PAS made of SiN, for example, is formed
(see FIG. 1B). The protective film PAS is a layer provided for
avoiding the direct contact of the thin film transistors TFT with
the liquid crystal LC and can prevent the deterioration of the
characteristics of the thin film transistors TFT.
[0061] On an upper surface of the protective film PAS, the pixel
electrode PX is formed at a center portion of each pixel region
except for a slight periphery of the pixel region. The pixel
electrode PX is formed of a light transmitting conductive film made
of, for example, ITO (Indium Tin Oxide), ITZO (Indium Tin Zinc
Oxide), IZO (Indium Zinc Oxide), SnO.sub.2 (Tin Oxide),
In.sub.2O.sub.3 (Indium Oxide).
[0062] Further, the pixel electrode PX is connected with the
above-mentioned contact portion of the source electrode ST via a
through hole formed in the protective film PAS in the vicinity of
the source electrode ST of the thin film transistor TFT. Due to
such a constitution, the video signal from the drain signal line DL
is supplied to the pixel electrode PX through the thin film
transistor TFT which is turned on in response to the scanning
signal from the gate signal line GL.
[0063] Here, groove portions DR1 are formed in the pixel electrode
PX, wherein the groove portions DR1 are formed of a plurality of
slits formed in the region of the pixel electrode PX.
[0064] The pattern of these groove portions DR1 is constituted such
that, as shown in FIG. 1A, one pixel region is divided into upper
and lower regions using an imaginary line A which extends in the x
direction in the drawing which traverses the center of one pixel
region. In the upper region above the imaginary line A, the groove
portions DR1 are formed with an inclination of (-).theta..sub.B
with respect to the drain signal line DL and are arranged in
parallel in the y direction in the drawing at a substantially equal
interval. Further, in the lower region below the imaginary line A,
the groove portions DR1 are formed with an inclination of
(+).theta..sub.B with respect to the drain signal line DL and are
arranged in parallel in the y direction in the drawing at a
substantially equal interval. In this case, the angle .theta..sub.B
is set to 45.degree., for example. As another embodiment, the angle
.theta..sub.B may be set to a value close to 45.degree., that is, a
value within a range of 38.degree. to 47.degree.. In this manner,
the groove portions are formed in a straight line and are arranged
such that the groove portions change the direction thereof in the
vicinity of the center of the pixel. Although the pixel region is
divided in two in the vertical direction, the pixel region may be
divided in a multiple number in the vertical direction, for
example, in three or four or more. The same goes for a projection
pattern which will be explained later.
[0065] On the other hand, also in the pixel region which is
positioned on the leftmost side in the drawing and is allocated to
red (R), the groove portions DR1 having the substantially same
pattern are formed. In this case, in the upper region above the
imaginary line A, the groove portions DR1 are formed with an
inclination of (-).theta..sub.R with respect to the drain signal
line DL and are arranged in parallel in the y direction in the
drawing at a substantially equal interval. Further, in the lower
region below the imaginary line A, the groove portions DR1 are
formed with an inclination of (+).theta..sub.R with respect to the
drain signal line DL and are arranged in parallel in the y
direction in the drawing at a substantially equal interval. In this
case, the angle .theta..sub.R is set larger than the angle
.theta..sub.B when the angle .theta..sub.R is compared with the
angle .theta..sub.B, for example.
[0066] Further, also in the pixel region which is positioned at the
center in the drawing and is allocated to green (G), the groove
portions DR1 having the substantially same pattern are formed. In
this case, in the upper region above the imaginary line A, the
groove portions DR1 are formed with an inclination of
(-).theta..sub.G with respect to the drain signal line DL and are
arranged in parallel in the y direction in the drawing at a
substantially equal interval. Further, in the lower region below
the imaginary line A, the groove portions DR1 are formed with an
inclination of (+).theta..sub.G with respect to the drain signal
line DL and are arranged in parallel in the y direction in the
drawing at a substantially equal interval. In this case, the angle
.theta..sub.G is set larger than the angle .theta..sub.B,
.theta..sub.R when the angle .theta..sub.G is compared with the
angle .theta..sub.B, .theta..sub.R, for example.
[0067] Here, these respective groove portions DR1 are served for
dividing the inside of one pixel region into a plurality of domains
together with groove portions DR2 which are formed also on the
liquid-crystal-side surface of the transparent substrate SUB2. The
groove portions DR2 are explained later.
[0068] On the upper surface of the transparent substrate SUB1 on
which the pixel electrodes PX are formed as described above, an
orientation film ORI1 is formed in a state that the orientation
film ORI1 also covers the pixel electrodes PX. The orientation film
ORI1 is a film which is directly brought into contact with the
liquid crystal LC and the rubbing treatment may be applied to a
surface of the orientation film ORI1 to determine the orientation
direction of molecules of the liquid crystal LC.
[0069] In the cross-sectional view shown in FIG. 1B, the
transparent substrate SUB2 which is arranged to face the
transparent substrate SUB1 in an opposed manner with the liquid
crystal therebetween is shown. On a liquid-crystal-LC-side surface
of the transparent substrate SUB2, black matrixes BM are formed to
define the respective pixel regions. That is, the black matrixes BM
which are formed in a liquid crystal display part (a region which
is constituted of a mass of the pixel regions) adopt a pattern in
which an opening is formed in a center portion of each pixel region
thus enhancing the contrast of the display.
[0070] Further, the black matrixes BM are formed to sufficiently
cover the thin film transistors TFT on the transparent substrate
SUB1 side and interrupt the radiation of an external light to the
thin film transistors TFT thus avoiding the deterioration of
characteristics of the thin film transistors TFT.
[0071] On the surface of the transparent substrate SUB1 on which
the black matrixes BM are formed, color filters CF are formed in a
state that the color filters CF cover the openings of the black
matrixes BM. Here, the color filter CF is formed of a green (G)
filter. This is because that the pixel is a pixel which is
allocated to green (G). Accordingly, the red (R) color filter CF is
formed on the leftmost-side pixel region in the drawing and the
blue (B) color filter CF is formed on the rightmost-side pixel
region in the drawing.
[0072] On the surface of the transparent substrate SUB1 on which
the black matrixes BM and the color filters CF are formed, a
leveling film OC is formed in a state that the leveling film OC
also covers the black matrixes BM and the color filters CF. The
leveling film OC is a resin film which can be formed by coating and
is provided for eliminating stepped portions which become apparent
due to the formation of the black matrixes BM and the color filters
CF.
[0073] Further, the groove portions DR2 are formed in a surface of
the leveling film OC. A pattern of the groove portions DR2 is shown
in an overlapped manner in FIG. 1A. As viewed in a plan view, the
pattern of the groove portions DR2 is arranged parallel to the
above-mentioned groove portions DR1 formed on the transparent
substrate SUB1 side and, at the same time, there exists the
relationship that the groove portion DR2 is arranged between the
neighboring groove portions DR1 or the groove portion DR1 is
arranged between the neighboring groove portions DR2.
[0074] Accordingly, the angle of the groove portions DR2 is equal
to angle .theta..sub.B of the groove portions DR1 in the blue (B)
pixel, the angle of the groove portions DR2 is equal to angle
.theta..sub.R of the groove portions DR1 in the red (R) pixel, and
the angle of the groove portions DR2 is equal to angle
.theta..sub.G of the groove portions DR1 in the green (G)
pixel.
[0075] Here, on an upper surface of the leveling film OC, a light
transmitting conductive film similar to the pixel electrode PX is
formed and this conductive film constitutes a counter electrode CT
which is used in common with respect to the respective pixel
regions.
[0076] An orientation film ORI2 is formed on a surface of the
counter electrode CT, wherein the orientation film ORI2 is a film
which is directly brought into contact with the liquid crystal LC,
and the rubbing treatment maybe applied to a surface of the
orientation film ORI2 for determining the orientation direction of
the molecules of the liquid crystal LC.
[0077] With respect to the above-mentioned liquid crystal display
device, in three color pixels, a plurality of domains are formed
due to the groove portions DR (DR1, DR2) which are formed in each
pixel, wherein the inclinations of the groove portions DR of these
domains are made different from each other.
[0078] Here, FIG. 10 shows a cross-section taken along a line X-X
in FIG. 1 in the region where the thin film transistor TFT is
formed.
[0079] FIG. 2 is a characteristic graph which shows the
relationship between an angle (electrode angle) of the groove
portions DR and the transmissivity when the electrode angle is
changed from approximately 37.degree. to approximately 55.degree.,
wherein a characteristic curve of the red (R) pixel (indicated by a
fine line in the drawing), a characteristic curve of the green (G)
pixel (indicated by a dotted line in the drawing) and a
characteristic curve of the blue (B) pixel (indicated by a bold
line in the drawing) are respectively shown. Here, a liquid crystal
gap is set to 4.0 .mu.m.
[0080] As can be clearly understood from FIG. 2, it is found that
the transmissivity depends on the angle of the groove portions DR
and, at the same time, it is also found that the transmissivity is
lowered in order of the green (G) pixel, the red (R) pixel, the
blue (B) pixel when the angles of the groove portions DR in three
respective pixels are set equal.
[0081] Here, since the respective characteristics exhibit a curved
shape which has a maximum value in the vicinity of 43.degree. and
hence, by setting the angle of the groove portions DR in the blue
(B) pixel to 43.degree. or a value in the vicinity of 43.degree.
(for example, 38.degree. to 47.degree.) and by increasing or
decreasing the angles of the respective groove portions DR of the
red (R) pixel and the green (G) pixel than the above-mentioned
value (these angles may be set to the same value), it is possible
to approximate the transmissivities of the red (R) pixel and the
green (G) pixel to the transmissivity of the blue (B) pixel.
[0082] Accordingly, as explained in conjunction with the
above-mentioned embodiment, assuming the angle of the groove
portions DR in the blue (B) pixel as .theta..sub.B (for example,
38.degree. to 47.degree.), by setting the angle .theta..sub.R of
the groove portions DR of the red (R) pixel larger than the angle
.theta..sub.B, for example, and by setting the angle .theta..sub.G
of the groove portions DR of the green (G) pixel smaller than the
angle .theta..sub.B, for example, coloring in a white display state
can be eliminated. Further, since such an advantageous effect can
be obtained by changing the angles of the groove portions in
respective pixels, there is no possibility that the orientation
regulation force is weakened whereby it is also possible to
eliminate coloring in an intermediate gray scale display state.
[0083] Here, FIG. 3 shows a characteristic graph which corresponds
to the characteristic graph shown in FIG. 2 and shows the
relationship between the angle (hereinafter referred to as
electrode angle) of the groove portions DR and the transmissivity
when the electrode angle is changed from approximately 37.degree.
to approximately 55.degree. provided that the liquid crystal gap is
set to 4.2 .mu.m. Also in this case, the respective characteristic
curves are similar to the respective characteristic curves shown in
FIG. 2 and the transmissivity is lowered in order of the green (G)
pixel, the red (r) pixel and the blue (B) pixel.
[0084] Further, FIG. 4 also shows a characteristic graph which
corresponds to the characteristic graph shown in FIG. 2 and shows
the relationship between the angle (electrode angle) of the groove
portions DR and the transmissivity when the electrode angle is
changed from approximately 37.degree. to approximately 55.degree.
provided that the liquid crystal gap is set to 4.5 .mu.m. Also in
this case, the respective characteristic curves are similar to the
respective characteristic curves shown in FIG. 2 and the
transmissivity is lowered in order of the green (G) pixel, the red
(r) pixel and the blue (B) pixel.
[0085] This implies that the transmissivity with respect to the
electrode angle is not largely changed depending on the difference
of the liquid crystal gap and hence, by setting gradients of the
inclinations of the groove portions DR in respective pixels in
three respective pixels for color display as described in the
above-mentioned embodiment without being influenced by the value of
the liquid crystal gap, it is possible to reduce the influence
attributed to coloring.
[0086] Further, FIG. 5 is a graph in which the characteristics of
the respective pixels are plotted when the cell gap is set to 4.2
.mu.m, for example, wherein an x axis and a y axis which conform to
a characteristic graph based on so-called CIE 1931 are respectively
adopted as an x axis and a y axis of the graph, and the electrode
angle .theta..sub.R of the red (R) pixel, the electrode angle
.theta..sub.G of the green (G) pixel and the electrode angle
.theta..sub.B of the blue (B) pixel are respectively defined.
[0087] In the drawing, the characteristic indicated by a mark "x"
is obtained by the conventional constitution when the electrode
angles are set such that .theta..sub.R=45.degree.,
.theta..sub.G=45.degree., .theta..sub.B=45'. In the drawing, the
characteristic indicated by a mark ".DELTA." is obtained by the
constitution to which the technical concept of the present
invention is applied when the electrode angles are set such that
.theta..sub.R=45 .degree., .theta..sub.G=56 .degree.,
.theta..sub.B=45.degree.. In the drawing, the characteristic
indicated by a mark ".largecircle." is also obtained by the
constitution to which the technical concept of the present
invention is applied when the electrode angles are set such that
.theta..sub.R=52 .degree., .theta..sub.G=55.degree.,
.theta..sub.B=45.degree..
[0088] In this case, the desirable characteristic is indicated by a
mark "-" in the drawing, this characteristic is coincided with the
above-mentioned characteristic indicated by the mark
".largecircle.".
[0089] Here, in the above-mentioned embodiment, in the respective
pixels, the pixel region is divided into two regions using the
imaginary line which traverses the center in the x direction in the
drawing (the direction parallel to the gate signal line GL) and the
direction of the groove portions DR is made different in respective
regions. However, it is not always necessary to divide the pixel
region into these two regions. That is, in the respective pixels,
the directions of the groove portions DR are respectively directed
in one direction and this direction is finely changed for the red
(R) pixel, the green (G) pixel and the blue (B) pixel respectively.
It is because that even in such a case, it is possible to ensure
the division of the pixel into a plurality of domains.
[0090] Further, the above-mentioned embodiment describes the case
in which the angle of the groove portions DR of the red (R) pixel
with respect to the drain signal line DL is set as .theta..sub.R,
the angle of the groove portions DR of the green (G) pixel with
respect to the drain signal line DL is set as .theta..sub.G and the
angle of the groove portions DR of the blue (B) pixel with respect
to the drain signal line DL is set as .theta..sub.B and these
angles are made different from each other.
[0091] However, when the spaced-apart distance (the distance which
is directed downwardly in the direction perpendicular to respective
grooves which face each other) of the groove portions DR1 and the
groove portions DR2 is equal with respect to the pixels of
respective colors, the difference in the above-mentioned angles
.theta..sub.R, .theta..sub.G, .theta..sub.B is also made to
correspond to the difference in distances of respective grooves
along an imaginary line parallel to the gate signal lines GL. In
other words, the distance between the neighboring groove portions
DR1 and the distance between the neighboring groove portions DR2
along the imaginary line which traverses the groove portions DR1,
DR2 arranged in parallel differ among the red pixel, the green
pixel and the blue pixel.
[0092] As can be clearly understood from FIG. 2, FIG. 3 and FIG. 4,
the advantageous effect of the present invention that the coloring
is eliminated can be realized by setting the inclination of the
groove pattern for the blue pixels larger or smaller than the
inclinations of the groove patterns for the red pixels and the
green pixels. This is because that the difference in brightness of
the respective colors can be reduced. It is further desirable that
the inclinations of the projection patterns or the groove patterns
of the pixels are set to satisfy any one of following relationship.
It is because that such a relationship can further reduce the
difference of brightness among respective colors.
[0093] 1) blue pixel<red pixel<green pixel
[0094] 2) blue pixel>red pixel>green pixel
[0095] 3) red pixel<blue pixel<green pixel
[0096] 4) green pixel<blue pixel<red pixel
[0097] The groove pattern may be constituted of an electrode
forming portion and an electrode non-forming portion. That is, the
advantageous effect of the present invention that coloring is
eliminated can be realized by providing the electrode non-forming
portion in the electrode pattern. Due to such a constitution, the
electrical groove pattern can be formed. Further, this groove
pattern is also capable of functioning as the structural groove
pattern.
[0098] In place of the groove pattern, the projection pattern may
be formed. It is desirable that the projection pattern has a height
lower than a thickness of the liquid crystal layer.
[0099] FIG. 6A and FIG. 6B are constitutional views showing another
embodiment of the pixel of the liquid crystal display device
according to the present invention and correspond to FIG. 1A and
FIG. 1B, wherein FIG. 6A is a plan view and FIG. 6B is a
cross-sectional view taken along a line b-b in FIG. 6A.
[0100] The constitution which makes this embodiment different from
the constitution shown in FIG. 1 lies in that in place of the
groove portions DR2 formed on the liquid-crystal-side surface of
the transparent substrate SUB2 in FIG. 1, projecting portions PR
are formed in this embodiment as shown in FIG. 6. The angle
.theta..sub.B of the projecting portions PR for the blue (B) pixel,
the angle .theta..sub.R of the projecting portions PR for the red
(R) pixel and the angle .theta..sub.G Of the projecting portions PR
for the green (G) pixel have the substantially same relationship as
the relationship shown in FIG. 1.
[0101] This embodiment indicates that when one pixel region is
divided into a plurality of domains, the division may be performed
by either one of the groove portions DR and the projecting portions
PR. This is because that irrespective of the groove portions DR or
the projecting portions PR, the inclination of the respective
molecules of the liquid crystal in one domain is directed in the
direction opposite to the inclination of the respective molecules
of the liquid crystal in another domain arranged close to one
domain.
[0102] FIG. 7A and FIG. 7B are constitutional views showing another
embodiment of the pixel of the liquid crystal display device
according to the present invention, wherein FIG. 7A is a plan view
and FIG. 7B is a cross-sectional view taken along a line b-b in
FIG. 7A.
[0103] The pixel shown in FIG. 7 is basically configured such that
the pixel electrodes PX and the counter electrodes CT are formed on
the liquid-crystal-side surface of the transparent substrate SUB1
and, as viewed in a plan view, these electrodes respectively have a
comb-teeth shape and are arranged to be meshed with each other. An
electric field is generated between the pixel electrodes PX and the
counter electrodes CT and the transmissivity of light which passes
through them is controlled by the electric field. Accordingly, as
can be clearly understood from FIG. 7B, in this constitution, the
counter electrodes CT are not formed on the transparent substrate
SUB2 side.
[0104] Here, the patterns and the arrangement of the gate signal
lines GL, the thin film transistors TFT, the drain signal lines DL,
the insulation film GI as an insulation film to be stacked, the
protective film PAS and the like are provided in the substantially
same manner as the embodiment shown in FIG. 1.
[0105] Further, in this embodiment, the counter electrodes CT and
the gate signal lines GL are formed on the same layer and the pixel
electrodes PX are formed on the upper surface of the protective
film PAS in the same manner as the embodiments shown in FIG. 1 and
FIG. 6.
[0106] Here, the counter electrodes CT are formed integrally with a
counter voltage signal line CL which extends in the x direction in
the drawing at the center of the pixel region, wherein, for
example, three strip-like counter electrodes CT are formed in an
extended manner in the region above the counter voltage signal line
CL in the drawing, while three strip-like counter electrodes CT are
formed in an extended manner in the region below the counter
voltage signal line CL in the drawing in the same manner.
[0107] Then, the extending direction of the counter electrodes CT
from the counter voltage signal line CL is set to extend in the
(+).theta. direction with respect to the drain signal line DL in
the upper region of the pixel and in the (-).theta. direction with
respect to the drain signal line DL in the lower region of the
pixel. That is, in this embodiment, the behavior of the liquid
crystal is made opposite from each other between the upper region
and the lower region of the pixel so as to compensate for coloring
of the image which occurs depending on a viewing angle.
[0108] Further, the angle .theta..sub.B of the extending direction
of the counter electrodes CT in the blue (B) pixel, the angle
.theta..sub.R of the extending direction of the counter electrodes
CT in the red (R) pixel on the leftmost side in the drawing, and
the angle .theta..sub.G of the extending direction of the counter
electrodes CT in the green (G) pixel at the center in the drawing
are respectively made different from each other and have the
relationship .theta..sub.R>.theta..sub.G>.theta.- .sub.B, for
example, as shown in the drawing.
[0109] Although such a constitution is adopted for sufficiently
reducing the coloring also with respect to the display in the
intermediate gray scale in the same manner as the embodiment shown
in FIG. 1, the detailed explanation is made after the understanding
of the constitution of the pixel electrode PX.
[0110] Here, with respect to the counter electrodes CT, two counter
electrodes CT are respectively arranged close to the drain signal
lines DL which are arranged at both sides of the pixel region and
sides of these counter electrodes CT are formed parallel to the
drain signal lines DL and hence, the counter electrodes CT have an
approximately triangular shape. Such a constitution is adopted for
narrowing a gap between the counter electrode CT and the drain
signal line DL so as to avoid the leaking of light from the gap
and, at the same time, to ensure a sufficient shielding function by
making lines of electric force from the drain signal line DL
terminate at the counter electrode CT and by preventing the lines
of electric force from terminating at the pixel electrode PX.
[0111] The pixel electrodes PX are formed on the upper surface of
the protective film PAS as described above and the pixel electrode
PX is positioned between the counter electrodes CT and is arranged
parallel to the counter electrodes CT.
[0112] That is, these respective electrodes are respectively
arranged at an equal interval in order of the counter electrode CT,
the pixel electrode PX, the counter electrode CT, the pixel
electrode PX, . . . the counter electrode CT from the drain signal
line DL on one side to the drain signal line DL on another
side.
[0113] Accordingly, the extending direction of the pixel electrode
PX for the blue (B) pixel makes the angle .theta..sub.B with
respect to the drain signal line DL, the extending direction of the
pixel electrode PX for the red (R) pixel makes the angle
.theta..sub.R with respect to the drain signal line DL, and the
extending direction of the pixel electrode PX for the green (G)
pixel makes the angle .theta..sub.G with respect to the drain
signal line DL.
[0114] As described above, in such a constitution, the electric
field is generated between the pixel electrode PX and the counter
electrode CT and the direction of the electric field becomes, when
the respective electrodes are constituted relatively longer than
the interval between these electrodes, substantially perpendicular
to the extending direction of the electrodes. For example, when the
respective electrodes make the angle (+).theta. with respect to the
drain signal line DL, the direction of the electric field becomes
(-) (.pi./2-.theta.).
[0115] From the above, the direction of the electric field in the
blue (B) pixel, the direction of the electric field in the red (B)
pixel, and the direction of the electric field in the green (G)
pixel become different from each other.
[0116] Here, a cross section taken along a line XI-XI in FIG. 7 in
the region where the thin film transistor TFT is formed is shown in
FIG. 11.
[0117] Even when such a constitution is adopted, the angles of the
pixel electrodes PX and the counter electrodes CT correspond to the
angle of the groove portions DR (or the projecting portions PR) and
the transmissivity of the pixel differs depending on the angles in
the same manner as the embodiment shown in FIG. 1.
[0118] Accordingly, assuming the angle of the respective electrodes
in the blue (B) pixel as .theta..sub.B (for example, 38.degree. to
47.degree.), by setting the angle .theta..sub.R of the respective
electrodes of the red (R) pixel larger than the angle
.theta..sub.B, for example, and by setting the angle .theta..sub.G
of the respective electrodes of the green (G) pixel smaller than
the angle .theta..sub.B, for example, coloring in a white display
state can be eliminated. Further, since such an advantageous effect
can be obtained by changing the angles of the respective electrodes
in respective pixels, there is no possibility that the orientation
regulation force is weakened whereby it is also possible to
eliminate coloring in an intermediate gray scale display state.
[0119] The above-mentioned embodiment describes the case in which,
for example, the angle of the groove portions DR of the red (R)
pixel with respect to the drain signal line DL is set as
.theta..sub.R, the angle of the groove portions DR of the green (G)
pixel with respect to the drain signal line DL is set as
.theta..sub.G and the angle of the groove portions DR of the blue
(B) pixel with respect to the drain signal line DL is set as
.theta..sub.B and these angles are made different from each
other.
[0120] However, when the spaced-apart distance (the distance which
is directed downwardly in the direction perpendicular to respective
sides which face each other) of the groove portions DR1 and the
groove portions DR2 is equal with respect to the pixels of
respective colors, the difference in the above-mentioned angles
.theta..sub.R, .theta..sub.G, .theta..sub.B is also made to
correspond to the difference in the distance between the counter
electrodes CT and the pixel electrodes PX along an imaginary line
parallel to the gate signal lines GL. Here, the spaced-apart
distance between the counter electrodes CT and the spaced-apart
distance between the pixel electrodes PX are usually set equal
since a voltage corresponding to the spaced-apart distance is
obtained by the voltage applied to the respective electrodes.
[0121] FIG. 8 is a constitutional view showing another embodiment
of the pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 7A.
[0122] The constitution which makes this embodiment different from
the embodiment shown in FIG. 7A is as follows. First of all, the
drain signal lines DL are formed in a zigzag shape in the extending
direction thereof in a state that the drain signal lines DL are
arranged parallel to the pixel electrodes PX and the counter
electrodes CT which are bent using an imaginary line which extends
in the x direction in the drawing at the substantially center
portion of the pixel.
[0123] In conformity with such a constitution, out of three counter
electrodes CT, two counter electrodes CT which are arranged close
to the drain signal lines DL which are arranged on both sides of
the pixel region are respectively formed in a pattern in which the
width of the counter electrodes CT is uniform along the extending
direction.
[0124] Even with such a constitution, it is possible to make the
angle .theta..sub.R in the extending direction of the electrodes in
the pixel for red (R), the angle .theta..sub.G in the extending
direction of the electrodes in the pixel for green (G) and the
angle .theta..sub.B in the extending direction of the electrodes in
the pixel for blue (B) different from each other in the same manner
as FIG. 7A and hence, the same advantageous effect can be
obtained.
[0125] Here, since the inclinations of the electrodes of the pixels
for red (R), for green (G) and for blue (B) are different from each
other as described above, among the drain signal lines DL, some
drain signal lines are required to have sides which are arranged
parallel to the opposedly-facing sides of the neighboring counter
electrodes CT whereby there exist some drain signal lines DL which
increase or decrease a width thereof along the extending
direction.
[0126] FIG. 9 is a constitutional view showing another embodiment
of the pixel of the liquid crystal display device according to the
present invention and corresponds to FIG. 8.
[0127] The constitution which makes this embodiment different from
the embodiment shown in FIG. 8 is as follows. First of all, the
drain signal lines DL are formed in a zigzag shape while having a
uniform width. Further, the counter electrodes CT which are
arranged close to the drain signal lines DL are integrally
connected with each other between the pixel region and the
neighboring pixel region.
[0128] In other words, the counter electrode CT which has a width
larger than a width of the drain signal line DL is formed on the
drain signal line DL in an overlapped manner, wherein a portion of
the counter electrode CT which projects from one side of the drain
signal line DL is configured to function as the counter electrode
CT in one pixel region with respect to the drain signal line DL,
while a portion of the counter electrode CT which projects from
another side of the drain signal line DL is configured to function
as the counter electrode CT in another pixel region with respect to
the drain signal line DL.
[0129] In this case, the angle .theta..sub.R in the extending
direction of the electrodes in the pixel for red (R), the angle
.theta..sub.G in the extending direction of the electrodes in the
pixel for green (G) and the angle .theta..sub.B in the extending
direction of the electrodes in the pixel for blue (B) become
different from each other. Further, since the angles of respective
extending directions of the respective drain signal lines DL are
equal, among the counter electrodes CT which are overlapped to the
drain signal lines DL, there exist some counter electrodes CT which
increase or decrease a width thereof along the extending direction
as shown in FIG. 9.
[0130] The above-mentioned respective embodiments may be used in a
single form or in combination. It is because that the advantageous
effects of the respective embodiments can be obtained in a single
form or synergistically.
* * * * *